Miles per Gallon (US) to Liters per 100 Kilometers Converter | mpg (US) to L/100km

What this converter does

US fuel economy comes in miles per gallon, but a great deal of the world rates cars in litres per 100 kilometres. This converter takes a US mpg figure and turns it into L/100km. Enter the mpg value and read off the L/100km, so an American economy figure can be read the way Europe and many other places quote it.

A double change at once

This conversion does two things in one move, which is why it feels less obvious than most. First it changes the units, from miles and US gallons to kilometres and litres. Second, and more importantly, it flips the measure over: mpg counts distance per unit of fuel, where higher is better, while L/100km counts fuel per unit of distance, where lower is better. So a high mpg turns into a low L/100km. You are crossing from the imperial world to the metric one and turning the meaning inside out at the same time.

The rule and its constant

Because of that flip, the conversion is a division, not a multiplication:

L/100km = 235.215 ÷ mpg (US)

That constant, 235.215, is the number that rolls the whole thing together, both the unit change and the reciprocal, into one step. It is built on the US gallon of about 3.785 litres, so it only applies to US mpg; the UK figure uses a different constant. Divide 235.215 by the mpg and you have the L/100km.

A worked example

Say a car is rated at 30 mpg in the US and you want that in litres per 100 km.

• 235.215 ÷ 30 = 7.84 L/100km

So 30 US mpg is about 7.84 L/100km. In a market that quotes L/100km, that is the figure you would compare against other cars, and it sits in the middle of the range for an ordinary petrol car.

Common mpg (US) values in L/100km

As an anchor, 30 mpg US is about 7.84 L/100km, and a frugal 50 mpg US comes out near 4.7 L/100km.

What L/100km reveals that mpg hides

Look down the table and you will spot something mpg keeps hidden. Going from 15 to 20 mpg cuts the L/100km figure by almost 4 litres, from 15.68 to 11.76. But going from 50 to 60 mpg, the same 10 mpg jump further up, cuts it by less than 1 litre, from 4.70 to 3.92. The reason is that the relationship is a reciprocal, not a straight line. In real terms, this means improving a thirsty car saves far more fuel than improving an already efficient one, even for the same gain in mpg. Litres per 100 km shows that plainly, because it tracks the fuel you actually burn, which is one reason much of the world prefers it as a measure.

Questions people ask

How do I convert US mpg to L/100km?

Divide 235.215 by the US mpg figure. The conversion is a division because the two measures run in opposite directions.

Does it use the US or UK gallon?

The US gallon, about 3.785 litres, which is built into the 235.215 constant. UK mpg uses a different constant.

What is 30 US mpg in L/100km?

About 7.84 L/100km, a middle-of-the-road figure for an ordinary petrol car.

References

1. National Institute of Standards and Technology (NIST), Special Publication 811, Guide for the Use of the International System of Units (gallon definitions and unit conversions). https://www.nist.gov/pml/special-publication-811
2. U.S. Department of Energy and EPA, fueleconomy.gov (fuel economy ratings and fuel consumption information). https://www.fueleconomy.gov/